In the past, a practice that has been partially effective in overcoming the trouble has been to brush off the surface with a stiff steel brush, or to scrub it with a cement brick and wet sand or carborundum stone, thus partially removing the neat cement face in which the cracks develop. This remedy, however, is only temporary, the cracks being likely to appear months later. The brushing or scrubbing is merely an assistance, the real remedy being to keep the surface con tinuously and thoroughly wet as long as possible. For permanent results, the only effective remedy is to remove from the surface, as soon as the forms or moulds are taken down, as much of the excess of neat cement as possible; and then to allow the concrete to harden under conditions practically the same as when hardened under water—keeping it constantly wet during the hardening process by sprinkling, by covering with very wet sand, by inclosing in a very moist atmosphere, by immersing under water, or by some other convenient method of a similar char acter.
Efflorescence is the name commonly applied to the whitish scum sometimes appearing on stone, brick, terra-cotta, and concrete work, due to the leeching out of lime or other soluble chemical salts. If the scum is due to excess of cement it is known as laitance. The Sylvester process, consisting of alternate applications of hot soap and alum solutions, has proved effective in its removal. A wash of dilute hydrochloric acid (one part acid to forty parts water) will also be found effective. Efflorescence can be pre vented by waterproofing the exterior surface of the wall after the concrete has hardened.
In all concrete work, the essence of economy is found to lie largely in the proper proportion ing of ingredients according to the materials available and the work in hand, and in simplicity and duplication of forms. The designer—especi
ally of a reinforced structure—should therefore eliminate as far as possible all projecting mem bers such as beam panels, cornices, belt-courses, and offsets.
Owing to the comparative youth of this type of structure, it is only within very recent years that architects and engineers have given any very great attention to the development of de signs essentially suitable to reinforced con crete. It is the general practice to design in brick, stone, and steel, and then to call upon a reinforced concrete engineer to reproduce a structure in reinforced concrete. This is an im perfect and unscientific method, and unfair to the development of the true value of the con crete structure. Many architects and engineers are, as yet, too unfamiliar with the character istics of concrete to design a structure solely from that point of view. They think in terms of brick and steel, stone and wood, and design in these materials, and then attempt to adapt con crete to their structure. The architect who would design intelligently for reinforced concrete must think in terms of reinforced concrete, which possesses peculiar characteristics essentially its own. Any design which is to be carried out in this material should be adapted to its characteristics and qualifications. The reinforced concrete build ing must be essentially a plain building, and its architectural effect must be developed by the the study of the relation of the openings to the masses, together with the assistance of some surface finish suitable to the problem, or some color scheme, applied by the insertion, in the face of the structure, of tile, pebble, or mosaic work.